I have to agree with the OP in this case. Here is the translation of the plagiarized reply;
"The founder of HEXTA announced a $ 1 million reward for arresting Lukashenka or any other way to remove him from power."
The post does not explicitly suggest the writer was claiming ownership of the reply which is sort of common knowledge at the time. It's a news headline, and we regularly see different media houses use very similar headlines for their publications. If the op had written more which was copied without including a source, it would then be in the realm of plagiarism, imo.
The consequence being that if we don't class this as plagiarism, we then open the floodgates to dozens of accounts copy/pasting single lines of text, then citing this example as precedent as to why low effort posts are permissable. It doesn't matter if it's common knowledge, it has been copied verbatim without independent thought or comment.